Imaginality Create includes an Interaction Trigger called ‘Model Visible’, which will trigger an Interaction Result if a model is currently visible.
You can choose the model to be checking the visibility of – this defaults to the model selected in the ‘3D Models’ list.

For example, give the Dragon a Trigger of “Model Visible” with a Result of “Play Animation” of the Ninja for ‘Attack1′, then, whenever the Dragon is Visible, the Ninja will play an attack animation.
Then, add a second interaction that gives the Dragon a Trigger of “Model Invisible” with a Result of “Stop Animation” of the Ninja, then, whenever the Dragon disappears (is Invisible), the Ninja will stop its attack animation.